The field of the disclosure relates generally to a rotary machine, and more particularly to testing of a rotary machine, for example, a gas turbine, which, within the framework of an electrical energy production facility, rotates a generator connected to an electrical energy distribution network.
At least some known regulations impose constraints for the connection and synchronization of rotary machines with an interconnected electricity distribution network. These regulations are sometimes referred to as the “grid code.” Such regulations exist for each country or for geographic zones.
These regulations allow the development, maintenance, and usage of a coordinated, efficient, and economic electricity transmission system. Moreover, they ensure performance and reliability of the distribution network and elements which are connected to it for the country or geographic zone for which they are applicable.
These regulations or “specifications of the electricity distribution network manager” are based on technical aspects concerning connections of various elements to the network, but also on operation and use of a transport network, and particularly electrical lines and electrical facilities connected to the distribution network.
These regulations may specify that users are liable to provide the data required for planning and usage of the network, such as electricity demand forecasts, availability of electrical energy generation equipment, and the dates fixed for maintenance of large electricity generator assemblies.
In addition to the technical design aspects of a network, the “grid code” may define very specific operational criteria.
For example, it may relate to defining the rated frequency of the network, as well as the frequency variations accepted with regard to this rated frequency.
For example, in France, the electricity distribution network frequency is nominally 50 Hz and must be controlled within the limits of 49.5 to 50.5 Hz. For other countries, the rated frequency is of 60 Hz and must be between 59.5 and 60.5 Hz.
Furthermore, to participate in the primary setting of the network frequency, each network facility must provide to the network an active power reserve generally referred to as the “primary reserve.” For example, this reserve is equal to a percentage of the maximum power. Thus, each electrical energy generation unit participating in the setting of the network frequency has a proper margin of available power. By interconnection of the electrical networks, the total primary network corresponds to the amount of primary reserves of all the units participating in the primary setting of the frequency.
This primary reserve allows regaining balance between production and consumption and constitutes, from the various components enabling the primary setting of the frequency, the component with the shortest response time. In fact, in Continental Europe, part of the primary reserve must be mobilized in less than 15 seconds and the whole reserve in less than 30 seconds.
Furthermore, the electricity generation units are fitted with speed regulator devices which enable adapting their power according to the rotation speed of the rotary machine and, consequently, the network frequency. The mobilized part of the primary reserve is in proportion to the difference between the actual instant speed, represented by the measured frequency f, and the rated speed, corresponding to the set point frequency f0, according to the relation:δ=λ(f−f0)
where λ refers to the power setting of the unit.
On a 50 Hz network, it is not only necessary to know the response in power of the electricity generation units as a function of time, at a constant rotation speed of a rotary machine equipping the electricity generation unit, but also the capacity for limitation of the frequency drift over time at transient speeds.
In particular, an increase in the proportion of power supplied from renewable energy and fluctuations in the electricity demand in small electrical networks creates a need for increasing the dynamic response of combined cycles, at full load or at partial load, as well as for revising the response time of the electric network generation units.
Thus, tests are implemented on electric networks to demonstrate the actual capacity of the electricity generation units to respond to transient phenomena. However, it is necessary that these tests are carried out under very precise conditions. In practice, tests on an actual network are difficult to execute due to the operating conditions of the network. In fact, this type of test does not allow implemented tests under load outside the rated frequency of the network, if it is not deliberately degraded. It is also not possible to implement tests on a large scale without affecting the network users. Moreover, risks associated with any test failures and, thus, eventual disturbances or breaks in supply for all users, must be considered in relation to the benefits provided by execution of the test.
Furthermore, this type of test requires considerable resources in terms of electrical energy, fuel, and auxiliary fluids (for example, but not by way of limitation, oil and coolant). Also, the time required to prepare and execute tests under actual conditions may be considerable. Noise nuisance also should be considered when the test facilities are located near cities or other populated areas.
This is why some known gas turbine manufacturers use test benches to test the behavior of the turbines.
In this regard, U.S. Pat. No. 3,598,208 describes the use of a hydraulic brake to test the behavior of a gas turbine. In fact, in contrast to the connection of a turbine to an electrical network through a generator, the connection of a turbine to a hydraulic brake allows the turbine to operate at the rated frequency of the network, or at a lower or higher frequency.
Furthermore, the power of the shaft of a gas turbine coupled with a generator may be measured by a dynamometer or by a hydraulic brake, either by direct measure of the torque between the power turbine and the driven equipment or the power at the generator outlet, or by indirect measurement, calculation of the power of the gas turbine compressor.
Also, U.S. Patent Publication No. 2003/0011199 describes the regulation of valves to control air flow entering a compressor of a gas turbine in order to control its speed, by acting, for example, on the adjustable valves when the frequency is less than the rated frequency of the network to obtain a gradual change of frequency till the rated frequency is attained.
Furthermore, U.S. Patent Publication No. 2007/0271929 describes a method of synchronizing the speed of a gas turbine with the frequency of a distribution network by controlling the action of the compressor in order to control the power generated by the turbine.
In European Patent No. 2,378,085, a control device is used to change the torque of the turbine to respond to a frequency fluctuation on the electricity distribution network.
Furthermore, U.S. Pat. No. 8,191,410 describes a test bench in which a compressor is driven by a gas turbine in order to create a map of compression ratio and corrected air flows, which allows determination of corrected speed lines and the boundary conditions of compressor surge at full load and at partial load.
Finally, U.S. Pat. No. 8,452,515 describes simulation of the behavior of a gas turbine compressor.